Usb to usb file transfer linux

Figure 19: USB’s proc window snippet

Note that a pen drive belongs to a USB mass storage class, which expects a set of SCSI like commands to be transacted over the bulk endpoints. So, a raw read/write as shown in the code listing below may not really do a data transfer as expected, unless the data is appropriately formatted. But still, this summarizes the overall code flow of a USB driver. To get a feel of real working USB data transfer in a simple and elegant way, one would need some kind of custom USB device, something like the one available at eSrijan.

As a reminder, the usual steps for any Linux device driver may be repeated with the above code, along with the pen drive steps:

• Build the driver (pen_driver.ko file) by running make.
• Load the driver using insmod pen_driver.ko.
• Plug-in the pen drive (after making sure that usb-storage driver is not already loaded).
• Check for the dynamic creation of /dev/pen0. (0 being the minor number obtained – check dmesg logs for the value on your system)
• Possibly try some write/read on /dev/pen0. (Though you may mostly get connection timeout and/or broken pipe errors because of non-conformant SCSI commands)
• Unplug-out the pen drive and look out for gone /dev/pen0.
• Unload the driver using rmmod pen_driver.

Summing up

Meanwhile, Pugs hooked up his first of its kind creation – the Linux device driver kit (LDDK) into his system to show a live demonstration of the USB data transfers. “A ha! Finally a cool complete working USB driver”, quipped excited Shweta. “Want to have more fun. We could do a block driver over it”, added Pugs. “O! Really”, Shweta asked with a glee on her face. “Yes. But before that we would need to understand the partitioning mechanisms”, commented Pugs.

Notes

1. Make sure that you replace the vendor id & device id in the above code examples by the ones of your pen drive. Also, make sure that the endpoint numbers used in the above code examples match the endpoint numbers of your pen drive. Otherwise, you may get an error like “… bulk message returned error 22 – Invalid argument …”, while reading from pen device.
2. Also, make sure that the driver from the previous article is unloaded, i.e. pen_info is not loaded. Otherwise, it may give an error message “insmod: error inserting ‘pen_driver.ko’: -1 Device or resource busy”, while doing insmod pen_driver.ko.
3. One may wonder, as how does the usb-storage get autoloaded. The answer lies in the module autoload rules written down in the file /lib/modules/ /modules.usbmap. If you are an expert, you may comment out the corresponding line, for it to not get autoloaded. And uncomment it back, once you are done with your experiments.
4. In latest distros, you may not find the detailed description of the USB devices using cat /proc/bus/usb/devices, as the /proc/bus/usb/ itself has been deprecated. You can find the same detailed info using cat /sys/kernel/debug/usb/devices – though you may need root permissions for the same. Also, if you do not see any file under /sys/kernel/debug (even as root), then you may have to first mount the debug filesystem, as follows: mount -t debugfs none /sys/kernel/debug.

The author is a hobbyist in open source hardware and software, with a passion for mathematics, and philosopher in thoughts. A gold medallist from the Indian Institute of Science, Linux, mathematics and knowledge sharing are few of his passions. He experiments with Linux and embedded systems to share his learnings through his weekend workshops. Learn more about him and his experiments at https://sysplay.in.

About Anil Kumar Pugalia

The author is a hobbyist in open source hardware and software, with a passion for mathematics, and philosopher in thoughts. A gold medallist from the Indian Institute of Science, Linux, mathematics and knowledge sharing are few of his passions. He experiments with Linux and embedded systems to share his learnings through his weekend workshops. Learn more about him and his experiments at https://sysplay.in.

32 thoughts on “ USB Drivers in Linux: Data Transfer to & from USB Devices ”

Nice Article. Thanks a lot for sharing this info.

I tried the USB driver code. The data tranfer using “usb_bulk_msg” fails with error code “-8”. Please let me know if you have any comments on this?

Well like he already pointed out, if the EP-OUT and EP-IN are wrong, you will get that message.

Good tutorial, but would like to really understand the SCSI commands for a regular USB drive. Is it formatted specifically for each device?

No, it is not formatted specifically for each device. Rather as per the usb storage protocol.

HEllo sir, I’m wokin as a system developer (Trainee..)………………
I Searched many sites to know about Ldd , I failed to find a good one.
But u provide an awsome article about Ldd…
tanqs for dhat………..

all are FINE .
U -> pugs..
? -> swatha

Thanks for reading and appreciating my articles. Let’s KIT 🙂

THanks sir.
I hv one doubt about add a debug driver(xhci debug driver . v put som ‘printk’ to find the flow) to kernel…

-> i hv xhci.c filess and kernel 3.19(not compiled and installed yet) .
-> I also hv a compiled .ko file of .c files

to c log messeges

Can i replace the orginal .ko files (xhci .ko files) with mine at run time, Will it work?
Or should i replace .c files in uncompiled kernel with mine , and compile the kernel then c the log messages…>>.

Typically, replacing the original .ko by yours should work.

Typically, replacing the original .ko by yours should work.

Great to see person like Anil Kr Pugalia, for all his kind help

Thanks for your appreciation.

Everything was done perfectly, but how do I do to create a file (with a single character, for example) inside a pendrive recognized by this driver?

If you read the above comments, and mentions in the article, you’d realize that you cannot actually write into a pendrive using this driver. For that one needs to additionally implement the SCSI based usb storage logic in the read & write calls above. This driver just gives the framework for the same.

thank you sir for the artical can we see the output of the code

Check out the bullets above the “Summing Up” above. Especially, the 5th bullet, which talks about seeing some errors. Aren’t you getting the same?

I am using UBANTU 17.10 my pen drive intiate contol 0 but it’s not shown in storage

I assume you are referring to that with our driver it doesn’t show in storage. It wouldn’t. As it is not a complete storage driver. It is just to demonstrate the USB working. For a complete storage driver, you need to integrate the block & then filesystem driver over it. And block driver also over SCSI protocol layer, as USB storage protocol is based on SCSI.

Did you check as to who has acquired the pen driver? Do “cat /sys/kernel/debug/usb/devices” and check for the “Driver: …” row in the pen drive entry. It should be your driver. Typically it gets occupied by the usb-storage driver. You need to remove that and then re-plug your pen drive.

I tried your steps.
$ sudo rmmod uas
$ sudo rmmod usb-storage
$ sudo insmod pen_driver.ko
Now /dev/pen0 dynamically created, but i couldn’t read/write. I am getting following error

Attached the dmesg log for further information:
[ 8956.626947] usbcore: deregistering interface driver uas
[ 8957.996753] usbcore: deregistering interface driver usb-storage
[ 8969.531749] pen_driver: loading out-of-tree module taints kernel.
[ 8969.531770] pen_driver: module verification failed: signature and/or required key missing – tainting kernel
[ 8969.532086] Minor obtained: 0
[ 8969.532100] usbcore: registered new interface driver pen_driver
[ 9104.323168] Bulk message returned in read -110
[ 9115.587159] Bulk message returned in read -110
[ 9134.041047] Bulk message returned in read -32
[ 9135.725897] Bulk message returned in read -32

I hope I provided correct endpoints.

Please help me to do read/write with usb device. Need to maintain rawusb format or any format?

Thanks for your time.

Read the comments above.

Hi Anil Kumar Pugalia ,

Please add your suggestion. Seems like something went wrong at pen_read() function at my end.

Please read the comments above – it actually is not expected to read & write.

Sir plz at what extension we save this all code?

It is a continuation of the previous two articles. Follow to 12th & then from there to 11th article from the above link at the beginning of the article. And you’ll find the details.

Plz Sir where is the code of pen_driver.ko ?
When i enter make command it show me file not specified.

This article is a continuation of the previous two articles. Follow to 12th & then from there to 11th article from the above link at the beginning of the article. And you’ll find the details.

Thanks for Writing these beautiful articles on Linux Device Drivers…..
I made my Microcontroller STM32F103C8 a USB device ( POS ) and Successfully Emmurate that as HID.
Now I want to read the data of its Endpoint(0x81 or 0x01 0r 0x82 etc) and want to see at my STDOUT screen.
HOW CAN I DO THAT .

copy_to_user ( ) and copy_from_user ( ) and not worthy for me or maybe I am not able to use them properly..

Depending on what type of endpoints you have, use the appropriate usb_*_msg APIs. What exactly to send & recv should be based on the uC firmware you have written.

Additionally, you may have to remove an existing pre-loaded HID driver, if it has acquired the device. Also, it may need control endpoint interactions – not really sure about it in HID protocol.

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